The present disclosure relates to a static var compensator apparatus and an operating method thereof and, more particularly, to a static var compensator apparatus, which changes a structure where a Thyristor Switched Capacitor (TSC) for compensation of reactive power is connected to a power system, and an operating method thereof.
It is necessary compensate for reactive power both in a direct current (DC) transmission system and in an alternating current (AC) transmission system for a purpose of transmission of power. The reactive power indicates power which is not actually used and does not consume heat. The reactive power travels back and forth between power and an electric device but does not cause occurrence of energy, so it cannot be used. If reactive power increases, voltages may be significantly lowered in its transmission and therefore power may be cut off. In order to prevent the above problems, it is necessary to compensate for the reactive power appropriately.
To this end, a reactive power compensator is used in a transmission system. The reactive power compensator may be classified into a Static VAR Compensator (SVC), which uses a thyristor element to compensate for reactive power, and a Static Synchronous Compensator (STATCOM) which uses an Insulated Gate Bipolar mode Transistor (IBGT) element.
A general SVC system may include a Thyristor Switched Capacitor (TSC) supplying reactive power and a Thyristor Controlled Reactor (TCR) absorbing reactive power. The SVC system adjusts reactive power of the TSC and the TCR to supply reactive power to a power system or absorb reactive power. By doing so, the SVC system controls voltages, a power factor, and the reactive power in order to control the whole system, thereby improving stability of the power system.
FIG. 1 is a diagram illustrating power system connection of a TCR and a TSC comprising an existing SVC system.
As illustrated in FIG. 1, an existing SVC system 100 may include a TCR 110 and a TSC 120.
The TCR 110 includes three bidirectional thyristors 111, 112, and 113, and three reactors 114, 115, and 116.
The three bidirectionial thyristors 111, 112, and 113 and the three reactors 114, 115, and 116 may be connected to an AC power system 130 in a structure of delta connection. In this case, each of the three bidirectional thyristors 111, 112, and 113, and the three reactors 114, 115, and 116 configures any one of three phases which generate three-phase AC.
The TCR 110 switches on and off the three bidirectional thyristors 111, 112, and 113 to absorb reactive power of the AC power system 130.
The TSC 120 are configured to include three bidirectional thyristors 121, 122, and 123, and three capacitors 124, 125, and 126.
The three bidirectional thyristors 121, 122, and 123, and the three capacitors 124, 125, and 126 may be connected to the AC power system 130 in a structure of delta connection. In this case, each of the three bidirectional thyristors 121, 122, and 123, and the three capacitors 124, 125, and 126 configures any one of three phases which generate three-phase AC.
The TSC 120 switches on and off the three bidirectional thyristors 121, 122, and 123 to supply reactive power to the AC power system 130.
FIG. 2 is a diagram illustrating a relation between a grid voltage and a voltage applied due to a configuration of a TSC in FIG. 1.
A structure of delta connection is a structure in which one end of a coil connecting elements, such as a thyristor and a capacitor, is connected to one end of another coil, and a line drawn from a coil linking point is connected to a power system. A circuit configured in the structure of delta connection generates three-phase AC which indicates AC continuously occurring at 120 degree phase differential.
Referring to FIG. 2, one end X2 of a coil X is connected to one end Y1 of a coil Y. Another end Y2 of the coil Y is connected to one end Z1 of a coil Z, and the other end Z2 of the coil Z is connected to the other end X1 of the coil X.
In addition, the linking point of X2 and Y1 is connected to a power system L1 through a line, the linking point of Y2 and Z1 is connected to a power system L2 through a line, and the linking point of X1 and Z2 is connected to a power system L3 through a line.
A phase voltage Up is a voltage induced to each of the three coils. In FIG. 2, a phase voltage applied to the coil X is U31, a phase voltage applied to the coil Y is U12, and a phase voltage applied to the coil Z is U23.
A line voltage UL is a voltage applied to between lines which are adjacent to each other. In FIG. 2, a line voltage applied between a line L1 and a line L2 is U1˜2, a line voltage applied between the line 2 and a line L3 is U2˜3, and a line voltage applied between the line L1 and the line L3 is U1˜3.
As illustrated in FIG. 2, a phase voltage is equal to a line voltage in a structure of delta connection. That is, the relation Up=UL is established. Therefore, a line voltage of a power system is applied to each phase voltage of the TSC.
Each of a TCR and a TSC which configure the existing SVC system is in a structure of delta connection. Because the TCR adjusts a firing signal to be applied to a thyristor, the TCR must be in a structure of delta connection.
In the case of the TSC, however, if a phase voltage of the TSC becomes high, a greater number of thyristor elements used in the TSC is required and therefore the price of the TSC may increase. In addition, if a phase voltage of the TSC becomes high, an insulating level of a capacitor may increases so a capacitor element may have a greater volume and thus the price of the TSC may go up. Furthermore, in this case, a voltage applied to each configurable device becomes to increase, reducing device stability.